docs: def _dump_csv(self, rows):
          """Take a list of dicts and return it as a CSV value. The
  
          .. versionchanged:: 4.0.0
  
          :param list rows: A list of lists to return as a CSV
          :rtype: str
  
          """
          self.logger.debug('Writing %r', rows)
          csv = self._maybe_import('csv')
          buff = io.StringIO() if _PYTHON3 else io.BytesIO()
          writer = csv.DictWriter(
              buff,
              sorted(set([k for r in rows for k in r.keys()])),
              dialect='excel')
          writer.writeheader()
          writer.writerows(rows)
          value = buff.getvalue()
          buff.close()
          return value